Strange problem with 8-stable, VMWare vSphere 4 & AMD CPUs (unexpected shutdowns)

[Alan Cox]

On Wed, Feb 10, 2010 at 12:46 PM, Jeremy Chadwick
<freebsd at jdc.parodius.com>wrote:
[snip]

>
> I read what Andriy wrote to mean that the way FreeBSD utilises 4MB TLB
> on certain models of AMD processors is broken/quirky, and on those CPUs,
> users should stick to vm.pmap.pg_ps_enabled="0" (loader.conf).
>
>
No.  He said, "We don't do anything that strays from specifications."  So,
he is not saying that FreeBSD is doing anything broken.

Here is what I know.  Several of us, myself included, have been able to
reproduce either lockups or machine check exceptions when BOTH the machine
check driver and superpages are enabled on AMD family 10h processors.  There
have been no reports of this problem on either Intel or earlier AMD
processors.  Moreover, there is no evidence of instability in AMD family 10h
processors until the machine check driver is enabled.  By default, FreeBSD
8.0 enables superpages but disables the machine check driver.  So, running
natively, i.e., without virtualization, you shouldn't experience a problem,
unless you explicitly enable the machine check driver.  However, running on
top of a hypervisor, like vSphere 4, you might face a problem because the
hypervisor might enable machine check exceptions, regardless of what the
FreeBSD guest does.  I really don't know whether vSphere 4 enables machine
check exception or not.  If it does, then either you disable the use of
superpages in the FreeBSD guest, or you find a way to disable the machine
check driver in the hypervisor.

Both Andriy and I have reported this problem to people at AMD, but we
haven't yet received AMD's analysis.  These things take time.

Regards,
Alan